DE3938016A1 - N-vinyl acetamide purificn. to remove acet-amide by extn. - with aromatic hydrocarbon and conc. aq. salt soln. and use in polymer and poly-vinyl:amine prodn. - Google Patents

Abstract

Purificn. of N-vinylacetamide (I) contaminated with acetamide (II) is carried out by (a) extracting impure (I) with an aromatic hydrocarbon solvent (III) to give a soln. of (I) and a smaller amt. of (II) in (III), (b) contacting this soln. with a conc. aq. salt soln. (IV), and (c) sepg. the phases to give a purer (I)/(III) soln. Pref. (III) is benzene, toluene, xylene or ethylbenzene. (IV) contains NaCl, KCl, MgCl2 or CaCl2 and pref. is satd. In particular, (III) is toluene and (IV) is brine. The impure (I) is obtd. by condensation of (II) and acetaldehyde to ethylidene-bis-acetamide (VI), followed by pyrolysis. USE/ADVANTAGE - The (I) obtd. is pure enough for polymerisation and is claimed for use in the prodn. of poly(N-vinylacetamide) (V) by polymerisation in the aq. soln., either as soln. or emulsion in oil, and (V) is claimed for use in the prodn. of poly(vinylamine) by hydrolysing the amido gps. to amino gps. or amine salts.

Description

The invention relates to a method for cleaning of N-vinylacetamide, which ver used materials has been contaminated. After another Its aspect relates to an educational process of poly (N-vinylacetamide) that can be hydrolyzed, to make poly (vinylamine).

Considerable efforts are being devoted to research Development of economical processes for the synthesis of poly (vinylamine) which, depending on its molecular weight important in a wide variety of applications can, as in the manufacture of dyes or dye as a flocculant in the treatment of Slurries or as a viscosity agent in the paper industry position and petroleum production. The commercially attractive Most effective way to form poly (vinylamine) is through the hydrolysis of poly (N-vinylamides) by free Radical polymerisation of N-vinylamides the. The most common for the production of polyvinylamines N-vinylamine used is N-vinyl acetamide. N-vinyl acetate amide can be obtained by condensation of acetamide and acetaldehyde are made to make ethylidene-bis-acetamide len, which is then pyrolyzed.

Because of the nature of the pyrolysis reactions, this is because of this Processed N-vinylacetamide with the starting materials of the reaction or with intermediate products uncleaned. For example, this is due to the pyrolysis of Ethylidene-bis-acetamide produced with N-vinylacetamide one mole of acetamide per mole of N-vinylacetamide cleans. It turned out that because of the proximity of the boilers  points of these two materials a clean separation pretty much by conventional distillation processes is difficult. In addition to the existing acetamide often also some minor impurities such as 1,1-diacetamide-hexa-2,4-diene, crotonaldehyde and N-acetyl-1,5-hexatrienylamine. Impurities like Crotonaldehyde caused by the self-condensation of acet aldehydes result, are radical inhibitors and be affect the polymerization adversely. This Verun cleaning causes a considerable reduction in the Molecular weight of the polymer and the polymer yield, if they are present in the polymerization mixture. It therefore, a high purity monomer is required to Polymers with high molecular weight and high yield synthesize, and the monomer is of high purity also required to control the polymerizations performable way.

U.S. Patent 40 18 826 (1977) describes the reaction of acet aldehyde with acetamide and the subsequent pyrolytic Cracking the ethylidene-bis-acetamide thus formed to Form N-vinylacetamide, which then to poly (N-vinylacet amide) is polymerized. The resulting polymer can be hydrolyzed with mineral acid to give the amine salt of To form polymers used in the manufacture of dye fen and colorants is advantageous. It is fixed ensures that N-vinylacetamide passes through before polymerization Distillation, fractional crystallization or ions exchange can be separated and cleaned.

US-PS 42 55 548 (1981) on the other hand describes in Example 1 a comprehensive cleaning process, the requ is necessary to N-vinylacetamide with polymerization to maintain activity. This N-vinylacetamide, which is made by Pyro Lysis of ethylidene-bis-acetamide was made through multiple solvent-solvent discharge  cleaned with large amounts of water and ether and nine continuous extractions followed by one after the other the following washing with water and brine and after that subsequent drying of the product with sodium sulfate and mag nesium sulfate were used.

US-PS 44 01 516 (1983) also deals with the Pro With the separation of "Acetamidethylen" (N-Vinylacet amide) from the pyrolysis products of ethylene-bis-acetamide. The solution to the problem proposed here is Ver Improvement of the distillation by adding a high boil the polyols, such as glycerin.

Overberger and Kikyotani, Journal of Polymer Science, Polymer Chemistry Edition, 21, 525-540 (1983) report on the purification of N-vinylacetamide by recrystalli isopropyl alcohol followed by column chromatography graphite on silica gel with ethyl acetate elution. These Citation states that only a polymer with ge low molecular weight (MW = 1000-3000) is obtained, if the monomer is not purified first. That from separation procedures proposed in this document is not practical on a commercial scale. The Chromato graphic separation of a commercial product required extremely high cost and produces the product after the Chromatography over a large volume of the solid adsorbent as a dilute solution in a solvent.

Stackman and Sommerville, Industrial Engineering Chemistry, Product Research Division 24, 246-252 (1985) recognizes the difficulty in cleaning N-vinyl acetamide, which is produced by a two-stage process that starts with acetaldehyde and acetamide. It will described a cleaning process that involves pouring the Pyrolysis product in ethyl ether to acetamide and ethyli precipitate the bis-acetamide, one being dark  brown solution of N-vinylacetamide remains. It's getting firm asked that a number of other solvents be substituted for ethyl ether, including toluene, it was tried however, none was beneficial. Further cleaning the Ether solution was purified by subsequent column chromatography Phie, treatment with charcoal and distillation leads. It is found that the monomer is not good polymerizes if any of these steps are omitted has been.

Japanese Patent Application, Publication No. 61-65 853 (1986) describes the use of wash water and alcohol, ester or ketone solvents in one Extraction column to separate the N-vinylacetamide, by thermal decomposition of ethylidene-bis-acet amide was produced. This application states that N-vinylacetamide not with non-polar solvents, such as Hydrocarbons can be extracted.

Other routes to N-vinylacetamide are proposed by US Pat. No. 4,554,377 (1986) which describes the preparation of N-vinylacetamide by pyrolysis of N- ( α- alkoxyethyl) acetamide, which was prepared from dimethylacetal and acetamide. An example describes the purification of N-vinyl acetamide, which was produced by pyrolysis of N- ( α- methoxyethyl) acetamide, by diluting the product with methanol and then treating it with activated charcoal.

US Pat. No. 4,567,300 (1986) describes the use of a basic catalyst for acetaldehyde to react with formamide to obtain N- ( α- hydroxyethyl) formamide, which can then react with primary or secondary alcohol over an acid catalyst to give N - Generate ( α- alkoxyethyl) formamide, which can then be thermally converted to N-vinylform amide.

No publication from the state of the art described above Technology describes a process for cleaning N- Vinylacetamide, which is contaminated with acetamide, on one Way that economically on a kommer target process can be transferred.

According to the present invention, N-vinylacetamide can be used Polymerization quality can be made by N-vinyl Acetamide is cleaned, which in its manufacture with Acetamide and possibly other organic materia l was contaminated. The cleaning process includes the extraction of the contaminated N-vinyl acetamide with an aromatic hydrocarbon solvent such as Toluene to a solution of the N-vinylacetamide and a ge less amount of contaminating materials in the Koh to form hydrogen sulfide, and the subsequent ß contact this solution with a concentrated aqueous saline solution and the separation of the aq saline solution from the hydrocarbon Solution to improve a solution of N-vinylacetamide with ter purity in this hydrocarbon solvent receive.

The invention also provides a method of formation of poly (N-vinylacetamide)

• a) Condensation of acetamide and acetaldehyde to ethyl to produce the bis-acetamide;
• b) pyrolysis of the ethylidene bis-acetamide product from step ( a ) to form a contaminated N-vinylacetamide product;
• c) dissolving the N-vinyl acetamide from the product of step ( b ) in toluene to form a first solution;
• d) separation of the first solution from the existing unsolvable one material;
• e) contact of the first solution with brine to a second Form solution of N-vinylacetamide in toluene;
• f) separation of the second solution from the brine, the Contains acetamide;
• g) extraction of the second solution with water to a to form aqueous solution of N-vinylacetamide; and
• h) polymerization of the N-vinylacetamide in the aqueous Solution, either as a solution or as an emulsion in oil.

The purified N-vinylacetamide, which thereby becomes poly (N vinyl acetamide) has been polymerized by hydrolysis easily converted to poly (vinylamine). At this The amide portions in the polymer in Amingrup are hydrolysed pen or amine salts converted.

While the purification process of this invention is advantageous in the purification of N-vinyl acetamide when acetamide is used in the manufacturing process, it is particularly valuable if the manufacturing route is the reaction of acetaldehyde and acetamide to form ethylidene-bis-acet amide, which is then pyrolyzed to N-vinylacetamide as described in U.S. Patent 4,018,826. However, other possible routes to N-vinylacetamide include the reaction of dimethyl acetal and acetamide to form N- ( α -methoxyethyl) acetamide, or the reaction of acetaldehyde and acetamide over a basic catalyst to form N- ( α- hydroxyethyl) acetamide form, which can then be converted to N- ( α- alkoxyethyl) acetamide and pyrolyzed to N-vinyl acetamide. In these processes, acetamide is the largest contaminant, e.g. B. about 40 wt .-%. Also in significant amounts, e.g. B. about 8 wt .-%, ethylidene-bis-acetamide is present, which remains unconverted in the pyrolysis step. Heavier by-products in significant quantities (greater than 2% by weight) are also often present.

The majority of the acetamide contaminants are called insoluble materials by filtration or decanting by treating the crude N-vinyl acetamide with a aromatic hydrocarbon such as toluene removed. The Amount of aromatic hydrocarbon present should be sufficient to complete the N-vinylacetamide dig, and ratios on the order of 5: 1 to 30: 1 on weight bases are workable. It is preferred that the extraction be at a ratio of about 5 to 15 parts by weight of the hydrocarbon, preferably as toluene, to a part of N-vinylacetamide becomes. It was found that a ratio of 10: 1 den Loss of N-vinyl acetamide during the subsequent Steps minimized while lower ratios too lead to substantial losses of N-vinylacetamide.

Other aromatic hydrocarbon solvents can are used, such as benzene, xylene or ethylbenzene. Although any isomer of xylene can be used most commonly the ortho, meta and para isomers as Mixture present in a commercially available solvent.

After the solvent treatment with the aromatic Hydrocarbon contains the hydrocarbon solution purified N-vinyl acetamide, e.g. B. about 85% purity or more, depending on the moisture content of the N-vinyl acetamids. The lower the moisture content, the more extraction efficiency of N-vinyl is higher acetamids resulting from this extraction step and preferably the moisture content in the N-vinyl  acetamide less than about 1% (all percentages given Rates are based on weight unless otherwise is marked).

In the second step, the N-vinylacetamide solution in aromatic hydrocarbon with a concentrated, aqueous, saline solution, e.g. B. an aqueous solution the chlorides of sodium, potassium, calcium or magnesium or any combination. These Solution must be concentrated, i. H. at least 80% sati gung, and it is preferred that the solution be complete is saturated to minimize the loss of NVA. The preferred solution for this step is sodium chloride brine. This wash step with brine ent removes much of the remaining acetamide and heavier By-products. The use of small amounts of brine is very important to a high recovery of the N-vinyl to maintain acetamids. For this reason, the Ver ratio of the N-vinyl acetamide present in the solution The amount of brine used on a weight basis is so small be as possible while most of it remains the acetamids and heavy by-products removed becomes. For toluene solutions, e.g. B. about 10% NVA and 3% Acetamide can contain a ratio of about 1: 1 to 5: 1 NVA to brine and preferably 3: 1 to 4: 1 used will. For the best recovery of N-vinylacetamide after washing with brine contains aromatic hydrocarbon solution with N-vinylacetamide a purity of more than 96%. This solution can be done directly for solution polymerization or for reverse emulsion poly merization are used, or an aqueous solution of N-Vinylacetamide is made simply by extracting the toluene solution made with water. On the other hand, can the solid N-vinyl acetamide by removing the solution by means of reduced pressure or by recrystallization tion at -30 ° C for 12 h. The addition  a non-polar hydrocarbon such as hexane convenient crystallization at higher temperatures, and 0 to 20 ° C. This will make the crystalline N-vinyl acetamide with a purity in the range of 95 to 97% hold.

If necessary, the purity can even be increased more, e.g. B. to more than 99%. The N-vinyl Acetamide with higher purity can be added Steps are made that involve the extraction of the N-Vinylacetamids in water, washing the aqueous N- Vinylacetamide solution with a small amount of one does not miscible, polar solvent, such as methyl t-butyl ether, ethyl t-butyl ether or diethyl ether, for removal further impurities, and the subsequent Ab separation of the ether from the extracted non-saline gene, aqueous solution. This solution can then polymerized or with the addition of other comonomers co be polymerized. A monomer with an even higher purity unit can be added by adding a soluble one inorganic salt, such as sodium chloride, for extraction th and separated aqueous solution, creating a high concentrated saline solution is formed, the N-Vinylacet contains amide, and extraction of this saline solution with methy Lenchlorid be produced. The methylene chloride is then removed, and N-vinylacetamide with a purity of at least 99% is won.

This cleaning process to N-vinylacetamide with poly merisation quality is simple, effective and efficient capable and can easily be transferred to commercial size will. The separation of the acetamide enables the Recycle the raw materials that are not have reacted to the initial reaction with acetaldehyde. The Aromatic hydrocarbon solvents can if separated and reused. It's from  particular advantage that the filtrate, which is the highly pure Contains N-vinylacetamide, directly to solution polymerization NEN or by extraction with water in an aqueous Solution polymerization or reverse emulsion polymer tion can be used using surfactants can.

Example 1

This example illustrates the typical cleaning of the raw N-Vinylacetamids (NVA) according to this inven such as the NVA, which is obtained by pyrolysis of ethylidene acetamide was obtained.

100 g of the raw NVA pyrolysis product (about 55% purity) and 450 g of toluene are placed in a 1000 ml beaker. The resulting mixture becomes good at 25 ° C for 30 minutes touched. The yellow toluene solution becomes insoluble Solids decanted with 2 × 40 g of fresh toluene getting washed. The toluene solutions are combined and washed with 20 g of brine. The yellow brine solution is poured off. The final toluene solution contains NVA with 96% purity, as determined by gel chromatography Analysis was shown. The NVA solid is replaced by Re crystallization isolated at -30 ° C for 12 h. The pure unit of this crystalline NVA is 96% as it passes through magnetic resonance analysis was found. NVA with higher purity (greater than 99%) will follow through isolated from the additional steps. The toluene solution will after washing with brine with 4 × 100 ml of water extracted. This aqueous solution is then with 20 ml Back extracted ethyl ether. This ether solution is removed poured. The aqueous solution is then mixed with sodium chloride saturated and extracted with 4 × 250 ml methylene chloride.  

After removing the methylene chloride at reduced NVA pressure is obtained with 99% purity.

Example 2

This example illustrates the importance of the monomer purity for the polymer yield in the following Polymerizations.

The raw pyrolysis is placed in a 2 l 3-neck round bottom flask product of N-vinyl acetamide, partially purified or highly purified N-vinylacetamide, toluene and 2,2'-azo bis (isobutyronitrile) initiator, AIBN. As before described, NVA is obtained with 99% purity. The Polymerizations are carried out under stick for 4 hours at 65 ° C atmosphere carried out. During the polymerization the polymer precipitates. At the end of the reaction, the right the resulting mixture is filtered. The granular polymerpro Products are washed with acetone and dried. The We The monomer unit on the polymer yield is in Table 1 shown.

Table 1

Effect of the impurities on the polymerization of NVA in toluene

As shown by the information in Table 1 the monomer purity has a significant effect on the off Prey of poly (N-vinyl acetamide).

Example 3

The monomer purity also has a strong effect on the molecular weight of the polymer formed, as is is shown by this example.

The polymerizations are carried out as in Example 2 leads, except that instead of toluene water as a solution medium is used. The polymers are precipitated lung isolated from acetone. The effect of monomer purity on molecular weight is shown in Table 2.

Table 2

Effect of the impurities on the polymerization of NVA in H₂O

Since this example illustrates solution polymerization, the molecular weight of the polymer is an average value. A polymer of N-vinylacetamide with a very high mole  Specular weight can be achieved by reverse emulsion polymerization will hold, and the impact of monomer purity is equally important in these processes.

Example 4

The following example shows the cleaning and the quick Polymerization of NVA by extraction and recrystallization tion from toluene / hexane. It also shows the disadvantages using too much brine when using Wash step with toluene.

Raw NVA, 56 lbs (25.4 kg) from the pyrolysis of Ethylidene-bis-acetamide containing about 35% NVA was found at 50 melted in seven proportions up to 60 ° C. Except for the first Fractions were each consecutive with the second Toluene extract from the previous fraction, then with the first toluene extract from the previous fraction and finally with a two times greater amount of fresh Toluene extracted. In each case, the slurry 0.5 h quickly stirred and the yellow supernatant liquid removed. These nine final toluene extracts contained from 5 to 19% NVA (18.5 lbs (8.39 kg)) and 0.6 up to 4.2% acetamide. The efficiency of NVA extraction was determined to be greater than 90%.

Each fraction was in a ratio of 7.2 to 10 parts by weight of the organic phase to a part of the Brine contacted with brine, separated and concentrated to about 30% NVA at reduced pressure. Hexane was added to each fraction until the turbidity point was reached (about 65% of the original vol mens), and these solutions were dropped to 0 ° C overnight chilled to precipitate the product. The crystalline The product was then decanted and filtered  separated, washed with hexane and under vacuum Room temperature dried. Representative groups were analyzed with approximately 97% NVA and 2% acetamide. The Polymerization at a weight ratio of 9: 1 from Vinyl acetate and NVA under nitrogen at 60 ° C required 0.15 to 0.2 mol% of an initiator to within one Hour to get a response.

The total yield of NVA was 8.7 lbs (3.95 kg) or 47%. The brine washes also included 7.2 lbs (3.27 kg) NVA (39% of the total). By white Extraction with toluene was possible with NVA from the brine solutions are removed.

The present invention provides a purified monomer of N-vinylacetamide, which is for use in the emulsion or solution polymerization is suitable for using polymers good yield and high molecular weight. The Invention enables the use of the starting material lien acetamide and acetaldehyde to form N-vinylacetamide the one that is then controlled in a commercial manner Scope can be cleaned and polymerized.

Claims (14)

1. Process for the purification of N-vinylacetamide, which is contaminated with acetamide, characterized by the extraction of the contaminated N-vinylacetamide with an aromatic hydrocarbon solvent in order to dissolve the N-vinylacetamide and a smaller amount of the contaminants therein Form solvent, contact this solution with a concentrated, aqueous, saline solution and separation of the aqueous, saline solution and the hydrocarbon solution to get a solution of the hydrocarbon solvent containing N-vinylacetamide with improved purity. 2. The method according to claim 1, characterized records that the aromatic hydrocarbon Substance solvent benzene, toluene, xylene or ethyl is benzene. 3. The method according to claim 1 or 2, characterized ge indicates that the saline solution an aqueous solution of the chloride salt of sodium, Is potassium, magnesium or calcium. 4. The method according to any one of claims 1 to 3, characterized characterized that the saline Solution is saturated. 5. The method according to any one of the preceding claims characterized by that Hydrocarbon solvent toluene and the aqueous Solution is brine.   6. The method according to any one of the preceding claims characterized in that the ver unpurified N-vinylacetamide by condensation of Acetamide and acetaldehyde product is made to order Form ethylidene-bis-acetamide followed by pyrolysis of ethylidene-bis-acetamide. 7. Process for further purification of N-vinylacetamide, that was cleaned according to claim 1, thereby ge indicates that at least part the solution of the hydrocarbon solvent that Contains N-vinylacetamide with improved purity Water is brought into contact with an aqueous, non-saline solution to form the N-Vinylacet contains amide and impurities, this aqueous, non-saline solution extracted with diethyl ether to dissolve the impurities in the ether Ether from the extracted, non-saline, aqueous gene solution is separated, the extracted and removed separated, aqueous solution a soluble, inorganic Salt is added to a highly concentrated salt form solution containing N-vinylacetamide, this Saline solution is extracted with methylene chloride, the Methylene chloride is removed and N-vinylacetamide with at least 99% purity is obtained. 8. The method according to claim 7, characterized records that the hydrocarbon solution medium toluene, the saline solution NaCl brine, the soluble inorganic salt NaCl and the salt solution is saturated with NaCl. 9. Process for the preparation of poly (N-vinylacetamide), characterized by:

• a) condensation of acetamide and acetaldehyde to produce ethylidene-bis-acetamide;
• b) pyrolysis of the ethylidene bis-acetamide product from step ( a ) to form a contaminated N-vinylacetamide product;
• c) dissolving the N-vinyl acetamide from the product of step ( b ) in toluene to form a first solution;
• d) separation of the first solution from the existing insoluble material;
• e) contacting the first solution with brine to form a second solution of the N-vinyl acetamide in toluene;
• f) separation of the second solution from the brine containing acetamide;
• g) extracting the second solution with water to form an aqueous solution of N-vinylacetamide; and
• h) polymerization of the N-vinylacetamide in the aqueous solution either as a solution or as an emulsion in oil.

10. The method according to claim 9, characterized records that the weight ratio of Toluene to N-vinylacetamide in the range from 5: 1 to 30: 1 lies and the weight ratio of N-vinylacetamide to the brine is in the range of 2: 1 to 5: 1. 11. Process for the preparation of poly (vinylamine), characterized by the formation of Poly (N-vinylacetamide) by the method according to An Proverb 9 and hydrolysis of the poly (N-vinyl acetamide) to the amide proportions in the polymer to amine groups or amine to convert salt. 12. The method according to claim 9, characterized in that the acetamide is recovered from the brine from step ( f ) and recirculated to step ( a ). 13. The method according to claim 9, characterized indicates that the aqueous solution of the N- Vinylacetamids before the polymerization of the N-vinyl acetamids in the aqueous solution with a non miscible, molar solvent is extracted. 14. The method according to claim 13, characterized shows that the immiscible, polar Solvent diethyl ether, methyl t-butyl ether or Is ethyl t-butyl ether.